The discovery and ability to isolate pluripotent stem cells that can give rise to mesoderm, endoderm and ectoderm lineages provides one foundation for emerging field of regenerative medicine. One of the first pluripotent stem cells of this type to be discovered and isolated is the embryonic stem (ES) cell. ES cells are cells derived from embryos, including human embryos, that are able to differentiate into the mesoderm, endoderm and ectoderm lineages under the proper conditions. The pluripotent nature of these cells makes them attractive candidates for cellular and/or tissue based regenerative medicine therapies. However there is much ongoing work relating to how best to differentiate these cells, reproducibly and efficiently into one or more desired lineages. Cell lineages and/or tissues generated and/or engineered from ES cells have utility both in vivo, for example in a transplant setting to replace a defective or non-existent cell lineage or tissue, and in vitro, for example as a research tool for screening candidate therapeutic agents.
As an example, differentiation of ES cells into cardiomyocytes would have great clinical significance. Transplantation of cardiomyocytes could be used in the treatment of cardiovascular disease. The major obstacle to cardiomyocyte transplant however is the need for donor cells and/or tissue which can only be gotten by organ donation. Thus, there is always a shortage of such cells.
Cardiomyocytes have been generated from ES cells. Analysis of gene expression profiles during ES cell differentiation in vitro suggests that the this process recapitulates cardiomyocyte development in vivo. ES cell derived cardiomyocytes when introduced into infracted hearts in animal models were able to survive, fuse with surrounding tissue, and be retained in the host. ES cell derived cardiomyocytes would therefore be ideal candidates for clinical transplantation therapy, provided sufficient numbers of these cells could be produced.